Skywatcher 190MN / fitting of a Moonlite focuser

[Gunnar]

Hello,

I am working with mounting of a Moonlite CR-2" focuser on my Skywatcher 190-MN. I got an idea, maybe i should make a useful thread for others who intend to fit a Moonlite on this tube. So this thread will describe my work until finished and hopefully fully collimated.

I also ordered the Orion 190-MN install kit. Lets see how it goes.

Gunnar

[Gunnar]

Hi,

Lets start with removal of the skywatcher crayford focuser.. easy step, 4 screws.

[Gunnar]

Skywatchers focuserbase hole diametre is 78mm! Can be useful information if you are trying to mount other focusers than a Moonlite and want to reuse the skywatcher base.

Here is the picthure of the new Moonlite CR-2" (drawtube2") and the Orion 190-MN install kit. I think it will be wery nice on a black 190-MN.

[Gunnar]

The MN-190 is a closed tube. The Orion 190-MN install-kit must be screwed from the inside of the tube. Therefore it is necessary to take away the corrector lens from the tube when mounting the Moonlite focuser. Put tape strips close to the edge at the corrector flange, close to the 6 screwholes for marking of the position. Then unscrew the corrector lens, 6 screws. Do not forget to have the lens cap on for protecting the corrector lens. After this is done, remove the corrector lens carefully and put it on a safe place, have in mind that the secondary mirror will also come out together as a complete unit so be careful not damaging the secondary mirror.

[Gunnar]

After looking into the tube, I decided to clean the tube from loose debris using compressed air. Therefore I also dismantled the primary mirror to protect it.

[barkis]

EeeK! I know you're being ultra careful, but the proximity of that file, and Screwdriver to the mirror face is a bit worrying.

Ron.

[Gunnar]

Hehe. I can see it now! Folks.. stop reading this thread now, It might give you nightmares at nights.

[Gunnar]

Hi,

Now it's time to assemble the parts on the telescope. I found that the tube is made of aluminum 2mm. The Orion 190-MN mounting plate fits perfectly on this skywatcher 190-MN. Screws supplied in the kit fits skywatchers threaded holes. The screws are narrower than the thread in the tube and passes through into the mounting plate. I used a small amount of silicone gasket between the tube and the mounting plate as a dust seal. Tighten the screws with moderate force.

I also painted all the shiny screws inside the tube with black paint. holes

Gunnar

[Gunnar]

Hi,

Now I take a little break. It will be a glass of red wine and a good movie on TV.

To be continued.

Gunnar

[Earl]

Brave man

[Gunnar]

Now I took the opportunity to replace the secondary mirror holder center screw to prevent the secondary mirror to be able to come off in the event of too much adjustment on the three collimating screws. I turned a new screw that was about 7 mm longer than the original screw. I do not remember where I read that this could happen. But I tried it and yes, the center screw threads out completely before the three collimating screws reaches its lowest position. This would have the secondary to detach and fall into the tube. The secondary mirror must not become detached from its holder during collimation. A longer screw prevents this possibility. With new longer screw mounted, check that the secondary is pretty good straight set against its holder before the reassembly of the corrector lens on the telescope. This will give you a good starting position for collimation. If you choose not to replace the center screw, I recommend not to touch anything on the collimating screws for the secondary mirror for now.

The corrector lens and primary mirror ready for reassembly! Take notice of the small centre mark on the secondary mirror! What is it for? I've been thinking about this small circle. Previously I collimated the telescope with the secondary center marker as a reference to get the secondary correct but the telescope has not really performed the nice round stars that it has a reputation for. More about this later.

We can also see the collimation screws with the mysterious screw nr 4 between two of the 3 collimation screws. which only act as a locking pin to prevent the secondary mirror to rotate freely. We do not need to adjust that one.

Gunnar.

[Gunnar]

:hello2:Moonlite CR-2" on top.

Now I have a big smile on my face. This focuser rocks, much, much more solid than the standard dual crayford focuser.

[Gunnar]

COLLIMATION!

Hi,

Did I say this will be easy? I have no idea! However we must not be afraid of collimating our scopes. Lets see how it goes!

The primary mirror and the front corector is attached to the telescope again and collimation can be started. Here are my tools. From left my shiny homemade 2 "lasercollimator and the red whistle I bought from FLO. And a hurricane blower that will help me to breathe .. Even a simple little plastic collimator made ​​of a film canister.

Although I am wery proud of my homemade shiny laser (with plexi reflection disc!!). The red cheshire has become my favorite.

Gunnar.

[Gunnar]

Brave man

Thank you Earl!

[Gunnar]

First let me say that I am not a guru on collimation. However I found a good tutorial written by John Reed which describes how to use the Cheshire collimation tool. I previously collimated the telescope using the lasercollimator. But this time I will use my new Cheshire.

Cheshire eyepiece attached to the focuser.

[Gunnar]

1st pic.

Notice this small centre mark on the secondary mirror again! Previously I collimated the telescope with the secondary center marker as a reference to get the secondary mirror in correct position underneath the focuser.

2nd pic.

This is an old picture from earlier collimation Jun23/2011

photograph taken through the 2 mm hole in the film canister tool.

I always came to an end result something like this when I centered secondary mirror through its center circle as a reference. The result always ended with a secondary that was offset to the front of the telescope away from the primary mirror! This caused me a lot of gray hair. As I understand (the offset) should be offset towards the primary mirror, not away from it. The primary mirror's reflection in the secondary came of course, always close to the edge towards primary mirror with this method. I have not liked it. I can not think of another way to use the secondary center marker. If there is anything I missed here, please give me a clue!

Well, as I said, the picture is from 2011. I still wanted to include it for comparison. I will ignore the secondary mirror's center circle this time! Let's see how it goes!

[Gunnar]

Hello again!

This is the result after collimation. Time to get out and try the telescope! It's cloudy this evening. I will return with a report when I have tried the telescope.

Pic.1.

My Skywatcher 190-MN photographed through the plastic film canister collimation tool.

Pic.2.

Photographed through the Cheshire collimation tool. It is actually possible to see the secondary mirror's center circle just to the right of the cross-hair towards the primary mirror.

I look forward to any comments about this, please tell me. As I said, I'm no expert on collimation. Does this look good?

Thanks in advance and thank you for watching the thread.

Gunnar.

[Gunnar]

Hi,

Two days ago it was finally clear skies again. The image shows the telescope set up and running before darkness settled.

As I said before, the telescope has not really performed the nice round stars that it has a reputation for.

See this picthure of M51 from 2012-03-02,

Note the strange radiations around the bright star. I was really hoping that collimation would fix this problem. Unfortunately, it was disappointing to note that the problem still occurs when I tried to photograph a few bright stars. The telescope has not become worse but not better either. It remained now to consider what it can depend on. Is it pinched corrector, primary mirror or secondary mirror? Or what ...

[Gunnar]

This is a picture of Capella from the day before yesterday. Perhaps inappropriate because it is a double star but the defect occurs in other bright stars as well. It shows the strange radiations again.

I have been working with the telescope in the day to try to solve the problem and have just come in after a further test shooting!

To be continued ...

[wrinkly]

Very good and concise explanation, Gunnar.

Feel for you with your collimation? problems.

Fancy swapping an ST80 on an EQ1 for your outfit? Life is a lot simpler.

Absolutely certain either you or a board member will sort it out soon and then, being an astronomer, you'll find something else to fret about.

[Gunnar]

Hi Wrinkly, sorry but I already have one. you can see it on the picthure. The guidescope! maybe I just put the caps on the MN190 and use the ST-80 instead... But I think I have come closer to solving the problem with my MN190 now after yesterdays test shooting.

Gunnar

[Gunnar]

Finding the error.

As I said, I did some more work with the telescope yesterday to find the error. After consideration, I decided finally to dismantle the front corrector lens to ensure that it was not pinched. You could say that I was a little worried about this. The corrector lens is attached to the telescope with a black fastening ring and 6 screws. When this ring is remowed the lens can fall out!! It looks a bit scary on the pitchure not holding it. I was not sure about this but found that there is no way to tilt the corrector. The only thing that can be set on the corrector are the three radial supports, must probably be set up with a just enough play so that the corrector can not be pinched.

[Gunnar]

Here is the corrector dismantled. It is a heavy piece of glass! Next, I decided to remove the secondary holder from the center hole to see why it has been so difficult to rotate. I found that it was too tight in my opinion, perhaps this could be bad and squeeze too much against the corrector lens. When this was fixed, it was easy to rotate and adjust the secondary mirror. I was happy with that. After that I put everything back on the telescope.

[Gunnar]

Adjusting the radial supports. (White nylon-tip screw on the inner flange)

[Gunnar]

Soft pads on the back of the attachment ring. The ring is screwed with very little force.